The present invention relates to tape-based data storage, and more particularly, this invention relates to a high resolution tape directory (HRTD) which is stored at end of data (EOD) in an index partition.
Linear Tape File System (LTFS) is a file system that is implemented by using a partitioning function of a tape drive. In LTFS, a tape is divided into a plurality of partitions. Conventionally, two partitions are established, but there is no limit as to the number of partitions possible. Information on a file system is stored in a partition referred to as the Index Partition (IP). Data, which is the contents of one or more files, is stored in a partition referred to as the Data Partition (DP).
One reason to partition LTFS is the sequential nature of tape-based media, e.g., data stored to a tape must be accessed sequentially, from beginning to end or vice versa. In the data format of a tape, the writing of data is permitted only once if it is to be stored into the same partition. Meanwhile, subsequent data will also be erased when data is written by starting from some midpoint in the data.
When an update to a file is to be written to tape-based media, it is necessary to update the file system information relating to the data stored to the tape. Because of the format characteristics of any sequential access device on which the tape may be accessed, it follows that such information will be written once at the last position of the tape.
If there is only one partition, pointer information of the file system is acquired from the last logical position of the tape at each time the cartridge (housing the tape) is loaded. In some cases, it takes time to acquire the file system information. A known technique for solving the above problem is, in order to access the pointer information of a file system at a high speed immediately after the loading of a cartridge, to prepare a dedicated partition and store the file pointer information in this partition. In this way, it is possible to access the file-system pointer information on the tape at a high speed immediately after the loading of the cartridge.
One principal use of a conventional linear tape open (LTO) tape drive is for backup purposes. For example, when data written to the tape is read out, the necessity of randomly moving to (locating) data on the tape, such as sequentially transferring it from a certain specified location to the host, has been limited. The necessity of high-speed movement (locating) has been recognized in use in an Enterprise environment, such as a high performance storage system (HPSS), a virtual tape system (VTS), and/or a hierarchical storage management (HSM). In such use, a drive that has the ability to utilize the high resolution tape directory (HRTD) function in order to access a specified data location at a high speed, for example, IBM tape drive model TS1130/TS1140, is useful.
Tape directory (TD) is information that indicates, in detail, a location of data on a tape. This information is stored at a specified area on the tape, written at the time of cartridge unloading, and read out at the time of cartridge loading. The tape drive searches for the data through the tape on the basis of this location information. In standard LTO, this information is obtained by bisecting a tape in a longitudinal direction (which is referred to as TD) and is stored in a cartridge memory (CM), whereas in IBM tape drive model TS1130/TS1140, 64-divided detailed information sections (which is referred to as HRTD) are stored on the tape. Making more detailed location information available results in greater accuracy for determining the location of data stored on the tape, and also results in less time that is required to find the data on the tape. Therefore, the speed of accessing the data increases, which is beneficial to the art of data storage.
However, conventional LTO drives do not offer HRTD. Some reasons why it is not offered may include that the amount of HRTD information is too large to be stored in CM (which is only 8 KB), if a tape drive is in conformity to IBM's original format, such as TS1130/TS1140; and moreover, since LTO is an open standard, a storage location at a specified area on the tape is not defined therein. Also, the HRTD function is not as important if a tape drive is used primarily for backup purposes, as most tape drives typically are. In backup applications, the amount of time necessary to read data from a tape may not be the most important factor in choosing the tape storage over other methods and media.
However, in an LTO5 drive, which is a major use environment of the current linear tape file system (LTFS), a user may be able to read/write data on a tape, as well as data stored in other media formats, such as on a CD-R and/or a universal serial bus (USB) memory stick, via simple graphical user interface (GUI), such as drag and drop or by conducting command-line operation. For this reason, conventionally, time taken for accessing an arbitrary file on the tape is becoming more and more important in an LTO drive, as well as in other tape formats.
However, unlike the IBM tape drive model TS1130/TS1140, an LTO drive does not offer the HRTD function of pinpointing a data-read location at a high speed immediately after loading.